Data storage devices employing one or more rotating disks on which data is recorded are well known and are often referred to as disk drives. Disk drives provide a relatively low cost means for storing and accessing data. Typically, each disk includes magnetically recordable material on the opposed surfaces of a substrate. Each surface is divided into a number of concentric data tracks and each data track is further divided into a number of track sectors capable of storing a set quantity of information. Data is accessed by positioning a magnetic head over a selected data track while the disk is rotating. The magnetic head can then read or write data to or from track sectors of that data track. The magnetic heads are typically biased against the surface of the disk such that, as the disk rotates, a magnetic head "flies" on an air film above the disk.
One goal in the design of disk drives is to decrease seek time, which is defined as the average time that is required for the disk drive to find and access selected data. One means for decreasing seek time is to cause the rotating disks to spin more quickly. Increasing the rotational speed relative to the magnetic heads allows the magnetic heads to read or write to more data sectors in a given amount of time. Rotational speeds greater than 10,000 rpm are desired.
A concern with increasing the rate of disk rotation is that the increase in rotational speed is typically accompanied by an increase in vibration experienced by the disks. As data track widths become increasingly narrow, even small vibrational movements of the disks can cause the magnetic heads associated with the disks to become temporarily misaligned, causing read and/or write errors.
Many of the different sources of disk vibration can be categorized as mechanical sources relating to rotationally driving the stack of data disks. For example, a drive mechanism may include ball bearings for the purpose of providing a low-friction assembly, but the assembly still includes bearing-to-surface relative movements that induce vibrations. The vibrations may resonate through the elements of the drive mechanism and significant vibrations will be imparted to the disks. As a result, the performance of read and write operations are adversely affected.
Other sources of disk vibration may be categorized as aerodynamic. For example, as data disks of a disk stack are rotated, air in the gaps between adjacent disks is dragged along with the rotating disks and is accelerated outwardly toward the edges of the disks by centrifugal forces. The accelerated air is propelled from the cavities between the disks in an unorganized or random pattern. The rapid departure of pockets of air results in a low pressure region between adjacent disks that is then filled by air rushing to eliminate the vacuum. A discharge cycle causing chaotic and random flutter of the disks is created when the temporary vacuum causes a flex phase during which portions of the edges of the adjacent disks flex toward each other, followed by a release phase caused by air refilling the vacuum. The refilling may also result in relative overpressure, causing the disks to temporarily spread apart beyond the desired distance. This cycle occurs repeatedly and randomly in the gaps between all of the disks, and becomes increasingly significant as the disks of disk drives are spun more rapidly, are made increasingly thin, and are positioned increasingly closer together.
Disk drive designers have incorporated vibration-retarding mechanisms into current devices. One approach to offsetting the mechanical sources is to introduce vibration dampers, such as a damping polymer, at locations that are selected to reduce the likelihood that vibrations will transfer from one part to the next. Another approach is to replace ball bearings with fluid bearings, but improvements to the design of fluid bearings are needed.
An approach to reducing the effects of the aerodynamic sources is to form the disks of a more rigid substrate material, so that the disks are less likely to flex. However, this approach often leads to an increase in the cost of the disks.
What is needed is a device that at least reduces the vibrational instability often associated with high speed disk drives.